Immunology, Serology, and Immunohematology Review

Vocabulary flashcards covering key terms and concepts in Immunology, Serology, and Immunohematology/Blood Banking.

Innate immunity

Nonspecific immune defense present from birth that provides an immediate response with no memory.

Adaptive immunity

Specific immune response that develops after exposure and has memory, comprising humoral immunity and cell-mediated immunity.

Active immunity

Form of immunity where the body produces its own antibodies naturally through infection or artificially through vaccination, providing long-lasting protection.

Passive immunity

Form of immunity where antibodies are received from another source (such as transplacental IgG or immune globulin injection), offering immediate but short-lived protection without memory.

Neutrophils

First responders in the immune system responsible for phagocytosis of bacteria, representing the most abundant white blood cell type.

Macrophages

Phagocytic cells that serve as antigen-presenting cells (APCs) and secrete cytokines.

Dendritic cells

The most potent antigen-presenting cells (APCs) that link innate and adaptive immunity.

Natural Killer (NK) cells

Innate immune cells that kill virus-infected cells and tumor cells without prior sensitization.

B lymphocytes

Lymphocytes that mature in the bone marrow and differentiate into plasma cells (which produce antibodies) and memory B cells.

T lymphocytes

Lymphocytes that mature in the thymus and include Helper T ($\text{CD4}^+$), Cytotoxic T ($\text{CD8}^+$), and Regulatory T cells.

CD4+ Helper T cells

T cells that coordinate the immune response, secrete cytokines, activate B cells and cytotoxic T cells, and serve as the main target of HIV.

CD8+ Cytotoxic T cells

T cells that directly kill infected or abnormal cells via perforin and granzyme.

Eosinophils

Granulocytes involved in defense against parasites and in allergic reactions.

Basophils and Mast cells

Cells that release histamine and mediate Type I hypersensitivity reactions.

Primary lymphoid organs

Organs where lymphocyte maturation occurs, specifically the bone marrow for B cells and the thymus for T cells.

Secondary lymphoid organs

Organs including lymph nodes, spleen, and MALT where immune responses are initiated.

MHC Class I

Molecules found on all nucleated cells that present endogenous antigens to $\text{CD8}^+$ T cells.

MHC Class II

Molecules found on antigen-presenting cells (APCs) that present exogenous antigens to $\text{CD4}^+$ T cells.

Fab region

The antigen-binding fragment of an antibody that contains the variable regions.

Fc region

The crystallizable fragment of an antibody that mediates effector functions such as complement binding and binding to Fc receptors on phagocytes.

Variable region

The region of an antibody that forms the antigen-specific binding site.

Primary immune response

The initial immune response to an antigen, characterized by a slower onset, IgM predominance, and a lower antibody titer.

Secondary (anamnestic) immune response

A faster, stronger immune response dominated by IgG, mediated by memory B cells and class switching.

IgG

The most abundant immunoglobulin in serum ($\sim 75-80\%$), featuring $4$ subclasses (IgG1-4), and the only class that crosses the placenta.

IgM

The largest immunoglobulin (pentamer), which is the first antibody produced in a primary response, serves as an efficient complement activator, and indicates current or recent infection.

IgA

Immunoglobulin found in body secretions (saliva, tears, breast milk, mucosa) as a dimer that provides mucosal immunity.

IgD

Immunoglobulin found on the surface of B cells that plays a role in B cell activation and maturation.

IgE

Immunoglobulin with the lowest serum concentration that binds to mast cells and basophils, mediating Type I hypersensitivity and defense against parasites.

Classical pathway

Complement activation pathway triggered by antigen-antibody complexes (IgG or IgM), beginning with C1q.

Alternative pathway

Complement activation pathway triggered directly by microbial surfaces without requiring antibodies, involving Factor B, Factor D, and properdin.

Lectin pathway

Complement activation pathway triggered by mannose-binding lectin (MBL) binding to microbial carbohydrates.

Membrane Attack Complex (MAC)

The final complement complex composed of C5b-6-7-8-9 that lyses target cell membranes.

C3a and C5a

Complement fragments that act as anaphylatoxins to promote inflammation and chemotaxis.

C3b

Complement fragment that functions as an opsonin to enhance phagocytosis.

Precipitation

Serologic reaction where soluble antigen and soluble antibody interact to form a visible lattice.

Agglutination

Serologic reaction where particulate antigens (cells or latex beads) clump visibly in the presence of specific antibodies.

Flocculation

Serologic technique where an antigen-antibody complex forms a fine precipitate, such as in VDRL testing.

Complement fixation

Serologic technique that detects antibody presence by measuring complement consumption.

ELISA (Enzyme-Linked Immunosorbent Assay)

Technique where antibody or antigen is tagged with an enzyme, yielding a measurable color change upon substrate addition.

Western Blot

Confirmatory serologic test that separates proteins by size via electrophoresis and probes them with labeled antibodies.

Prozone

False-negative serologic result caused by antibody excess.

Postzone

False-negative serologic result caused by antigen excess.

Sensitivity

The ability of a test to correctly identify true positives, resulting in few false negatives.

Specificity

The ability of a test to correctly identify true negatives, resulting in few false positives.

Type I (Immediate/Anaphylactic) Hypersensitivity

IgE-mediated reaction leading to mast cell and basophil degranulation and histamine release.

Type II (Cytotoxic) Hypersensitivity

Reaction where IgG or IgM antibody binds to cell-surface antigens, activating complement or phagocytosis.

Type III (Immune Complex) Hypersensitivity

Reaction caused by antigen-antibody complexes depositing in tissues, activating complement, and inducing inflammation.

Type IV (Delayed-Type/Cell-Mediated) Hypersensitivity

T-cell mediated reaction with no antibody involved, exhibiting a delayed onset of $24-72\,\text{hours}$.

Autoimmunity

Condition characterized by the breakdown of self-tolerance, leading to an immune attack on self-antigens.

Rheumatoid Factor (RF)

Autoantibody (usually IgM) directed against the Fc portion of IgG, associated with rheumatoid arthritis.

ASO (Anti-streptolysin O) titer

Serologic test detecting antibody to streptolysin O, indicating recent Group A Streptococcus infection.

C-Reactive Protein (CRP)

Acute phase reactant serving as a nonspecific marker of inflammation or infection that rises faster than ESR.

VDRL/RPR

Nontreponemal flocculation screening tests for syphilis that can produce biologic false positives.

FTA-ABS/TPPA

Treponemal confirmatory tests for syphilis that are more specific than VDRL/RPR.

Widal Test

Agglutination test used for detecting typhoid fever by targeting Salmonella typhi O and H antigens.

Monospot Test

Heterophile antibody test used to screen for infectious mononucleosis caused by Epstein-Barr Virus.

Procalcitonin

Laboratory biomarker used as a marker for bacterial sepsis.

Cytokines

Small signaling proteins that mediate and regulate immunity, inflammation, and hematopoiesis.

Pattern Recognition Receptors (PRRs)

Innate immune receptors that recognize conserved microbial structures known as Pathogen-Associated Molecular Patterns (PAMPs).

Apoptosis

Programmed, regulated cell death with preserved membrane integrity that typically produces no inflammation.

Necrosis

Unregulated, pathologic cell death characterized by loss of membrane integrity and induction of inflammation.

Severe Combined Immunodeficiency (SCID)

Primary immunodeficiency caused by absent or defective T and B cell function, commonly called 'Bubble boy disease'.

DiGeorge Syndrome

Condition caused by thymic aplasia or hypoplasia ($\text{22q11}$ deletion) resulting in T cell deficiency, congenital heart defects, and hypocalcemia.

Bruton's Agammaglobulinemia

X-linked disorder caused by BTK gene mutation leading to defective B cell maturation and severe antibody deficiency in male infants.

Chronic Granulomatous Disease (CGD)

Defect in NADPH oxidase in phagocytes causing failure of the respiratory burst, resulting in recurrent catalase-positive infections.

Wiskott-Aldrich Syndrome

X-linked immunodeficiency with defective WASP gene characterized by the triad of thrombocytopenia, eczema, and recurrent infections.

Hyperacute rejection

Transplant rejection occurring within minutes to hours, driven by preformed antibodies against donor antigens.

Acute rejection

Transplant rejection occurring days to months post-transplant, primarily mediated by T cells.

Graft-versus-Host Disease (GVHD)

Condition where donor T lymphocytes attack recipient tissues; prevented in blood transfusion by irradiating cellular components.

Landsteiner's Rule

Immunohematology rule stating that healthy individuals possess ABO antibodies against the antigens absent from their own red blood cells.

Forward typing

Serologic procedure testing patient RBCs with known antisera (anti-A, anti-B) to identify RBC surface antigens.

Reverse typing

Serologic procedure testing patient serum with known reagent $A_1$ and B cells to detect ABO antibodies.

Bombay phenotype (Oh)

Rare genotype ($hh$) lacking H, A, and B antigens, producing anti-H, anti-A, and anti-B, and able to receive blood only from other Bombay individuals.

Direct Antiglobulin Test (DAT)

Test detecting antibodies or complement components already bound to patient RBCs in vivo.

Indirect Antiglobulin Test (IAT)

Test detecting unbound, free IgG antibodies in serum in vitro.

Check cells

IgG-coated RBCs added to negative AHG tests to confirm that AHG reagent was active and washing was adequate.

Major crossmatch

Compatibility testing combining patient serum with donor RBCs to detect recipient antibodies against donor cells.

LISS (Low Ionic Strength Saline)

Enhancement medium that reduces ionic strength, increases antibody uptake rate, and shortens incubation time.

Polyethylene glycol (PEG)

Enhancement medium that removes water molecules to concentrate antibodies and increase sensitivity for IgG antibodies.

Zeta potential

Electrostatic repulsive force between negatively charged RBCs created by sialic acid that prevents spontaneous RBC aggregation.

Sensitization

First stage of antigen-antibody reaction where antibody binds to antigen without visible agglutination.

Lattice formation

Second stage of antigen-antibody reaction where antibody-antigen cross-links create visible agglutination.

Elution

Technique that unbinds and removes antibodies from sensitized RBCs for identification.

Adsorption

Technique that removes specific antibodies from serum by binding them to RBCs bearing corresponding antigens.

Partial D

Qualitative variation in the D antigen missing one or more epitopes, allowing the individual to produce anti-D if exposed to normal D-positive cells.

Weak D

Quantitative variation characterized by fewer D antigen sites per cell, detectable via the indirect antiglobulin test (IAT).

Platelet refractoriness

Failure to achieve expected platelet count increment post-transfusion, frequently caused by HLA alloimmunization.

Apheresis

Procedure of removing whole blood, isolating a target component, and returning the remaining blood components to the donor or patient.